The present invention generally relates to the chemical treatment of casting molds, and more particularly to the recovery of Y.sub.2 O.sub.3 from used investment casting shell molds.
Yttrium oxide (Y.sub.2 O.sub.3) is an important and useful metal casting refractory. It is thermodynamically stable in the presence of most reactive engineering metals including titanium, titanium alloys, and columbium (niobium). General information regarding the use of Y.sub.2 O.sub.3 in metal casting processes is presented in Feagin, R. C., "Casting of Reactive Metals Into Ceramic Molds", Report of Sixth World Conference on Investment Casting, pp. 4:01-4:13, 1984: and Calvert, E. D., "An Investment Mold For Titanium Casting", United States Department of the Interior (Bureau of Mines), Report of Investigations No. 8541, 1981.
The use of Y.sub.2 O.sub.3 as a refractory material in investment casting processes normally involves the production of casting shell molds containing significant quantities of Y.sub.2 O.sub.3 in combination with other materials including hydrolyzed binders. Most often, silica binders are present in the molds, including tetraethyl ortho silicate. Once the casting process is completed, the molds are usually discarded. However, this is undesirable for both financial and environmental reasons. Recovery of Y.sub.2 O.sub.3 from the used shell molds would offer a significant cost savings, and eliminate disposal problems.
The present invention involves a method whereby Y.sub.2 O.sub.3 can be reclaimed from used investment casting shell molds which contain Y.sub.2 O.sub.3 in combination with other materials. The method is highly efficient and results in the recovery of up to 85% or more of the Y.sub.2 O.sub.3 originally present in the molds. Also, the recovered Y.sub.2 O.sub.3 has a purity level of nearly 100%. This is accomplished using a minimal number of process steps, as described in detail below.